This invention is concerned with a finish meter for measuring the thickness of a metal oxide coating or film, and in particular, a tin oxide coating on the sealing surface of a glass container. A tin oxide coating or film is formed on the surface of a glass container by passing the container, after exiting from a forming machine and while still hot, through a tunnel while injecting into the tunnel a flow of a tin oxide precursor such as tin tetrachloride. Upon contact of the glass container with the atmosphere in the tunnel, the film or coating of tin oxide is formed over the glass container; which serves as a base to which organic coatings are applied, to protect the glass container from abrasion and preserve the strength of the glass container.
A problem that is present when a tin oxide coating or film is applied to a glass container is that the presence of an excessive amount of tin oxide coating on the rim of a glass container adversely affects the torque removal characteristics of a closure on a filled and capped container. Although various apparatuses are known for detecting the presence of an imperfection in an object in the shape of the rim of the glass container or detecting and measuring the thickness of a tin oxide coating on the sidewalls of the container, or along the neck, bead area, and threads of the container, heretofore apparatuses have not been able to detect and measure the thickness of a tin oxide coating or film on the sealing surface of the glass container due to the mechanical limitations of their construction.
It will be appreciated from the foregoing that there is a significant need for a device for detecting and measuring the thickness of a metal oxide coating or film on the sealing contact surface of a glass container. Accordingly, an object of the present invention is to provide a finish meter for detecting and measuring the thickness of a metal oxide coating or film on the sealing contact surface of a glass container.